1. Field of the Invention
The present invention relates to an image forming apparatus such as a color printer, a color copier, a color facsimile, or a complex apparatus of these printer, copier and facsimile.
2. Description of the Related Art
Electrophotographic image forming apparatuses for forming color images on a recording material such as paper or film are known. In color image forming apparatuses, color images are generally formed by using toners of four colors as developers. As a result the number of structural components is larger and the size can be easily increased over those of the monochromatic image forming apparatuses. Moreover, the number of units produced within a unit time, that is, the speed during color printing, is reduced. Following the spread of personal computers, the number of cases where the image forming apparatuses are used as the so-called printers in connection with personal computers has increased, personalization of the image forming apparatuses has advanced, and in most cases they are conveniently disposed close to the product user. Therefore, with consideration for user's operability, the image forming apparatus is desired to have a small height, and a small, e.g., narrow, apparatus is preferred based on space considerations. Furthermore, to provide for personalization and maintenance cost reduction of the image forming apparatuses, the users themselves conduct maintenance or replacement of spent components of the apparatuses.
From the standpoint of increasing the printing speed in color image forming apparatuses, tandem-type image forming apparatuses in which a plurality of developing image units are disposed in close proximity to a plurality of photosensitive bodies disposed in a row, a monochromatic toner image is formed on each photosensitive body, and the toner images are successively transferred, thereby transferring a color image onto a recording material, have an advantage over the well-known single-drum system in which developing units of a plurality of colors are provided around one image transfer body and the photosensitive body is rotated by the developing units to transfer toner images developed with developing units, synthesize a color image on the photosensitive body, and transfer this image onto a recording material.
When such a tandem-type image forming apparatus is wished to be reduced in size, the length of the apparatus in the arrangement direction can be reduced by disposing the image-producing units, in which a photosensitive body and a developing unit are integrated, or an intermediate transfer unit at an angle, as described in Japanese Patent Application Laid-open No. 2002-139976, rather than horizontally inside the apparatus body. Furthermore, the apparatus is so configured that each unit can be detachably attached to the apparatus body through an opening provided in the apparatus body and can be replaced or maintained when necessary. When the image forming apparatus has such a plurality of units that are detachably attached to the apparatus body, the image shift occurs if the position of the units during attachment is not established. For this reason, as described in Japanese Patent Application Laid-open No. 2002-139976, one end of each unit is supported inside the apparatus body and the other end is supported with a holding unit provided so that it can be opened and closed on the apparatus body.
In image forming apparatuses employing an electrophotographic process, power supply is conducted from a high-voltage power supply unit provided inside the apparatus body to the members requiring power supply, such as charging rollers, developing rollers, and cleaning rollers provided in image producing units, or intermediate transfer rollers, intermediate transfer cleaning rollers, and secondary transfer rollers provided in the intermediate transfer unit.
In the apparatus described in Japanese Patent Application Laid-open No. 2002-139976, when the image producing units or intermediate transfer unit are pulled out from the apparatus body, the operations are difficult because the holing unit cannot be opened or closed unless the screws fixing the holding unit to the apparatus body are removed with a tool. The holding unit requires accurate positioning with respect to the apparatus body since it is responsible for positioning each unit in a closed state thereof. Furthermore, because the holding unit can be opened and closed with respect to the apparatus body, a clearance is provided between the holding unit and the units located inside the apparatus body to ensure smooth operations when the units located inside the apparatus body are positioned. For this reason, there is a certain looseness even when the holding unit assumes a closed position. Therefore, the relative position of the photosensitive body and image producing units differs, even if very little, from the expected one, thereby creating a risk of image transfer position shifting at the time color superposition transfer conducted during multicolor image formation. Such a shift in image transfer results in the appearance of defective images such as color shift. Furthermore, each component of the holding unit has to be strong because this unit supports the image producing units and intermediate transfer unit. As a result, the weight thereof rises when the rigidity is increased by using a metal plate or the like. For this reason, each component relating to opening and closing the holding unit is required to have a higher strength. Moreover, safety has to be provided in the opening and closing direction because the apparatus might be inadvertently toppled when the holding unit is released.